Network Working Group Daniel O. Awduche
Internet Draft UUNET Worldcom, Inc.
Expiration Date: August 1999
Lou Berger
FORE Systems, Inc.
Der-Hwa Gan
Juniper Networks, Inc.
Tony Li
Juniper Networks, Inc.
George Swallow
Cisco Systems, Inc.
Vijay Srinivasan
Torrent Networks, Inc.
February 1999
Extensions to RSVP for LSP Tunnelsdraft-ietf-mpls-rsvp-lsp-tunnel-01.txt
Status of this Memo
This document is an Internet-Draft and is in full conformance with
all provisions of Section 10 of RFC2026. Internet-Drafts are working
documents of the Internet Engineering Task Force (IETF), its areas,
and its working groups. Note that other groups may also distribute
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Internet-Drafts are draft documents valid for a maximum of six months
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To view the current status of any Internet-Draft, please check the
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Abstract
This document describes the use of RSVP, including all the necessary
extensions, to establish label-switched paths (LSPs) in MPLS. Since
the flow along an LSP is completely identified by the label applied
at the ingress node of the path, these paths may be treated as
tunnels. A key application of LSP tunnels is traffic engineering
with MPLS as specified in [3].
We propose several additional objects that extend RSVP, allowing the
establishment of explicitly routed label switched paths using RSVP as
a signaling protocol. The result is the instantiation of label-
switched tunnels which can be automatically routed away from network
failures, congestion, and bottlenecks.
Finally, we propose a number of mechanisms to reduce the refresh
overhead of RSVP. The extensions can be used to reduce processing
requirements of refresh messages, eliminate the state synchronization
latency incurred when an RSVP message is lost and, when desired,
eliminate the generation of refresh messages. An extension to
support detection of when an RSVP neighbor resets its state is also
presented. These extension present no backwards compatibility
issues.
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Internet Draft draft-ietf-mpls-rsvp-lsp-tunnel-01.txt February 19991. Introduction and Background1.1. Introduction
This document is a specification of extensions to RSVP for
establishing label switched paths (LSPs) in Multi-protocol Label
Switching (MPLS) networks. Several of the new features described in
this document were motivated by the requirements for traffic
engineering over MPLS (see [3]). In particular, the extended RSVP
protocol supports the instantiation of explicitly routed LSPs, with
or without resource reservations. It also supports smooth rerouting
of LSPs, preemption, loop detection, and a fast reroute option to
allow expedited service restoration under fault conditions.
Since the traffic that flows along a label-switched path is defined
by the label applied at the ingress node of the LSP, these paths can
be treated as tunnels. When an LSP is used in this way we refer to
it as an LSP tunnel.
LSP tunnels allow the implementation of a variety of policies related
to network performance optimization. For example, LSP tunnels can be
automatically or manually routed away from network failures,
congestion, and bottlenecks. Furthermore, multiple parallel LSP
tunnels can be established between two nodes, and traffic between the
two nodes can be mapped onto the LSP tunnels according to local
policy. Although traffic engineering (that is, performance
optimization of operational networks) is expected to be an important
application of this specification, the extended RSVP protocol can be
used in a much wider context.
The purpose of this document is to describe the use of RSVP to
establish LSP tunnels. The intent is to fully describe all the
objects, packet formats, and procedures required to realize
interoperable implementations.
All objects described in this specification are optional with respect
to RSVP. This document discusses what happens when an object
described here is not supported by a node.
Resilience and scalability are very important considerations in this
specification. When an LSP tunnel fails, a significant amount of data
can be lost. As a result, failure notification and service
restoration should be fast and reliable. Accordingly, a number of
features are provided to facilitate smooth reroute of LSP tunnels,
fast reroute of LSP tunnels through intermediate detour paths under
faults, and fast and reliable LSP tunnel teardown. A few new objects
are also defined that enhance management and diagnostics of LSP
tunnels.
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Internet Draft draft-ietf-mpls-rsvp-lsp-tunnel-01.txt February 1999
Several new RSVP objects and messages are used to reduced processing
requirements related to RSVP refresh messages and address the latency
and reliability of RSVP Signaling. First, an aggregate message is
proposed to reduce the message handing load. Second tokens are added
as a short hand method of identifying state. Third, procedures to
suppress refreshes are defined. Last a Hello protocol is defined to
detect loss of a neighbor's state.
These extensions may be used in part in combination. They may be
useful in other RSVP environments and may be supported independent of
other MPLS related RSVP extensions.
Throughout this document, the discussion will be restricted to
unicast label switched paths. Multicast LSPs are left for further
study.
1.2. Background
Hosts and routers that support both RSVP [1] and Multi-Protocol Label
Switching [2] can associate labels with RSVP flows. When MPLS and
RSVP are combined, the definition of a flow can be made more
flexible. Once a label switched path (LSP) is established, the
traffic through the path is defined by the label applied at the
ingress node of the LSP. The mapping of label to traffic can be
accomplished using a number of different criteria. The set of
packets that are assigned the same label value by a specific node are
said to belong to the same forwarding equivalence class (FEC) (see
[2]), and effectively define the "RSVP flow." When traffic is mapped
onto a label-switched path in this way, we call the LSP an "LSP
Tunnel". When labels are associated with traffic flows, it becomes
possible for a router to identify the appropriate reservation state
for a packet based on the packet's label value.
The signaling protocol model uses downstream-on-demand label
distribution. A request to bind labels to a specific LSP tunnel is
initiated by an ingress node through the RSVP Path message. For this
purpose, the RSVP Path message is augmented with a LABEL_REQUEST
object. Labels are allocated downstream and distributed (propagated
upstream) by means of the RSVP Resv message. For this purpose, the
RSVP Resv message is extended with a special LABEL object. Label
stacking is also supported. The procedures for label allocation,
distribution, binding, and stacking are described in subsequent
sections of this document.
The signaling protocol model also supports explicit routing
capability. This is accomplished by incorporating a simple
EXPLICIT_ROUTE object into RSVP Path messages. The EXPLICIT_ROUTE
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Internet Draft draft-ietf-mpls-rsvp-lsp-tunnel-01.txt February 1999
object encapsulates a concatenation of hops which constitutes the
explicitly routed path. Using this object, the paths taken by label-
switched RSVP-MPLS flows can be pre-determined, independent of
conventional IP routing. The explicitly routed path can be
administratively specified, or automatically computed by a suitable
entity based on QoS and policy requirements, taking into
consideration the prevailing network state. In general, path
computation can be control-driven or data-driven. The mechanisms,
processes, and algorithms used to compute explicitly routed paths are
beyond the scope of this specification.
One useful application of explicit routing is traffic engineering.
Using explicitly routed LSPs, a node at the ingress edge of an MPLS
domain can control the path through which traffic traverses from
itself, through the MPLS network, to an egress node. Explicit
routing can be used to optimize the utilization of network resources
and enhance traffic oriented performance characteristics.
The concept of explicitly routed label switched paths can be
generalized through the notion of abstract nodes. An abstract node is
a group of nodes whose internal topology is opaque to the ingress
node of the LSP. An abstract node is said to be trivial if it is a
singleton, that is if it contains only one physical node. Using this
concept of abstraction, an explicitly routed LSP can be specified as
a sequence of IP prefixes with subnet masks or a sequence of
Autonomous Systems.
The signaling protocol model supports the specification of an
explicit path as a sequence of strict and loose routes. The
combination of abstract nodes, and strict and loose routes
significantly enhances the flexibility of path definitions.
An advantage of using RSVP to establish LSP tunnels is that it
enables the allocation of resources along the path. For example,
bandwidth can be allocated to an LSP tunnel using standard RSVP
reservations and Integrated Services service classes [4].
While resource reservations are useful, they are not mandatory.
Indeed, an LSP can be instantiated without any resource reservations
whatsoever. Such LSPs without resource reservations can be used, for
example, to carry best effort traffic. They can also be used in many
other contexts, including implementation of fall-back and recovery
policies under fault conditions, and so forth.
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Internet Draft draft-ietf-mpls-rsvp-lsp-tunnel-01.txt February 19992. Overview2.1. LSP Tunnels
According to [1], "RSVP defines a 'session' to be a data flow with a
particular destination and transport-layer protocol." However, when
RSVP and MPLS are combined, a flow or session can be defined with
greater flexibility and generality. The ingress node of an LSP can
use a variety of means to determine which packets are assigned a
particular label. Once a label is assigned to a set of packets, the
label effectively defines the "flow" through the LSP. We refer to
such an LSP as an "LSP tunnel" because the traffic through it is
opaque to intermediate nodes along the label switched path.
A new RSVP SESSION object, called LSP_TUNNEL_IPv4, has been defined
to support the LSP tunnel feature. The semantics of this object,
from the perspective of a node along the label switched path, is that
traffic belonging to the LSP tunnel is identified solely on the basis
of packets arriving from the PHOP or "previous hop" (see [1]) with
the particular label value(s) assigned by this node to upstream
senders to the session. In fact, the IPv4 that appears in the object
name only denotes that the destination address is an IPv4 address.
2.2. Operation of LSP Tunnels
This section summarizes some of the features supported by RSVP as
extended by this document related to the operation of LSP tunnels.
These include: (1) the capability to establish LSP tunnels with or
without QoS requirements, (2) the capability to dynamically reroute
an established LSP tunnel, (3) the capability to observe the actual
route traversed by an established LSP tunnel, (4) the capability to
identify and diagnose LSP tunnels, (5) the capability to preempt an
established LSP tunnel under administrative policy control, and (6)
the capability to perform downstream-on-demand label allocation,
distribution, and binding. In the following paragraphs, these
features are briefly described. More detailed descriptions can be
found in subsequent sections of this document.
To create an LSP tunnel, the first MPLS node on the path -- that is,
the sender node with respect to the path -- creates an RSVP Path
message with a session type of LSP_Tunnel_IPv4 and inserts a
LABEL_REQUEST object into the Path message. The LABEL_REQUEST object
indicates that a label binding for this path is requested and also
provides an indication of the network layer protocol that is to be
carried over this path. The reason for this is that the network layer
protocol sent down an LSP cannot be assumed to be IPv4 and cannot be
deduced from the L2 header, which simply identifies the higher layer
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Internet Draft draft-ietf-mpls-rsvp-lsp-tunnel-01.txt February 1999
protocol as MPLS.
If the sender node has knowledge of a route that has high likelihood
of meeting the tunnel's QoS requirements, or that makes efficient use
of network resources, or that satisfies some policy criteria, the
node can decide to use the route for some or all of its sessions. To
do this, the sender node adds an EXPLICIT_ROUTE object to the RSVP
Path message. The EXPLICIT_ROUTE object specifies the route as a
sequence of abstract nodes.
If, after a session has been successfully established and the sender
node discovers a better route, the sender can dynamically reroute the
session by simply changing the EXPLICIT_ROUTE object. If problems
are encountered with an EXPLICIT_ROUTE object, either because it
causes a routing loop or because some intermediate routers do not
support it, the sender node is notified.
By adding a RECORD_ROUTE object to the Path message, the sender node
can receive information about the actual route that the LSP tunnel
traverses. The sender node can also use this object to request
notification from the network concerning changes to the routing path.
The RECORD_ROUTE object is analogous to a path vector, and hence can
be used for loop detection.
Finally, a SESSION_ATTRIBUTE object can be added to Path messages to
aid in session identification and diagnostics. Additional control
information, such as preemption, priority, and fast-reroute, are also
included in this object.
When the EXPLICIT_ROUTE object (ERO) is present, the Path message is
forwarded towards its destination along a path specified by the ERO.
Each node along the path records the ERO in its path state block.
Nodes may also modify the ERO before forwarding the Path message. In
this case the modified ERO should be stored in the path state block.
The LABEL_REQUEST object requests intermediate routers and receiver
nodes to provide a label binding for the session. If a node is
incapable of providing a label binding, it sends a PathErr message
with an "unknown object class" error. If the LABEL_REQUEST object is
not supported end to end, the sender node will be notified by the
first node which does not provide this support.
The destination node of a label-switched path responds to a
LABEL_REQUEST by including a LABEL object in its response RSVP Resv
message. The LABEL object is inserted in the filter spec list
immediately following the filter spec to which it pertains.
The Resv message is sent back upstream towards the sender, in a
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Internet Draft draft-ietf-mpls-rsvp-lsp-tunnel-01.txt February 1999
direction opposite to that followed by the Path message. Each node
that receives a Resv message containing a LABEL object uses that
label for outgoing traffic associated with this LSP tunnel. If the
node is not the sender, it allocates a new label and places that
label in the corresponding LABEL object of the Resv message which it
sends upstream to the PHOP. The label sent upstream in the LABEL
object is the label which this node will use to identify incoming
traffic associated with this LSP tunnel. This label also serves as
shorthand for the Filter Spec. The node can now update its "Incoming
Label Map" (ILM), which is used to map incoming labeled packets to a
"Next Hop Label Forwarding Entry" (NHLFE), see [2].
When the Resv message propagates upstream to the sender node, a
label-switched path is effectively established.
2.3. Service Classes
This document does not restrict the type of Integrated Service
requests for reservations. However, an implementation should support
the Controlled-Load service [4] and the Class-of-Service service, see
Section 4.8.
2.4. Reservation Styles
The receiver node can select from among a set of possible reservation
styles for each session, and each RSVP session must have a particular
style. Senders have no influence on the choice of reservation style.
The receiver can choose different reservation styles for different
LSPs.
An RSVP session can result in one or more LSPs, depending on the
reservation style chosen.
Some reservation styles, such as FF, dedicate a particular
reservation to an individual sender node. Other reservation styles,
such as WF and SE, can share a reservation among several sender
nodes. The following sections discuss the different reservation
styles and their advantages and disadvantages. A more detailed
discussion of reservation styles can be found in [1].
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Internet Draft draft-ietf-mpls-rsvp-lsp-tunnel-01.txt February 19992.4.1. Fixed Filter (FF) Style
The Fixed Filter (FF) reservation style creates a distinct
reservation for traffic from each sender that is not shared by other
senders. This style is common for applications in which traffic from
each sender is likely to be concurrent and independent. The total
amount of reserved bandwidth on a link for sessions using FF is the
sum of the reservations for the individual senders.
Because each sender has its own reservation, a unique label and a
separate label-switched-path can be assigned to each sender. This
can result in a point-to-point LSP between every sender/receiver
pair.
2.4.2. Wildcard Filter (WF) Style
With the Wildcard Filter (WF) reservation style, a single shared
reservation is used for all senders to a session. The total
reservation on a link remains the same regardless of the number of
senders.
A single multipoint-to-point label-switched-path is created for all
senders to the session. On links that senders to the session share, a
single label value is allocated to the session. If there is only one
sender, the LSP looks like a normal point-to-point connection. When
multiple senders are present, a multipoint-to-point LSP (a reversed
tree) is created.
This style is useful for applications in which not all senders send
traffic at the same time. A phone conference, for example, is an
application where not all speakers talk at the same time. If,
however, the reservation requested is greater than a single sender's
requirements, then the reserved bandwidth on links close to the some
senders may be greater than what is required. This restricts the
applicability of WF for traffic engineering purposes.
Furthermore, because of the merging rules of WF, EXPLICIT_ROUTE
objects cannot be used with WF reservations. As a result of this
issue and the lack of applicability to traffic engineering, use of WF
is not considered in this document.
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Internet Draft draft-ietf-mpls-rsvp-lsp-tunnel-01.txt February 19992.4.3. Shared Explicit (SE) Style
The Shared Explicit (SE) style allows a receiver to explicitly
specify the senders to be included in a reservation. There is a
single reservation on a link for all the senders listed. Because
each sender is explicitly listed in the Resv message, different
labels may be assigned to different senders, thereby creating
separate LSPs.
SE style reservations can be provided using multipoint-to-point
label-switched-path or LSP per sender. Multipoint-to-point LSPs may
be used when path messages do not carry the EXPLICIT_ROUTE object, or
when Path messages have identical EXPLICIT_ROUTE objects. In either
of these cases a common label may be assigned.
Path messages from different senders can each carry their own ERO,
and the paths taken by the senders can converge and diverge at any
point in the network topology. When Path messages have differing
EXPLICIT_ROUTE objects, separate LSPs for each EXPLICIT_ROUTE object
must be established.
2.5. Rerouting LSP Tunnels
One of the requirements for Traffic Engineering is the capability to
reroute an established LSP tunnel under a number of conditions, based
on administrative policy. For example, in some contexts, an
administrative policy may dictate that a given LSP tunnel is to be
rerouted when a more "optimal" route becomes available. Another
important context when LSP tunnel reroute is usually required is upon
failure of a resource along the tunnel's established path. Under
some policies, it may also be necessary to return the LSP tunnel to
its original path when the failed resource becomes re-activated.
In general, it is highly desirable not to disrupt traffic, or
adversely impact network operations while LSP tunnel rerouting is in
progress. This adaptive and smooth rerouting requirement
necessitates establishing a new LSP tunnel and transferring traffic
from the old LSP tunnel onto it before tearing down the old LSP
tunnel. This concept is called "make-before-break." A problem can
arise because the old and new LSP tunnels might compete with other
for resources on network segments which they have in common.
Depending on availability of resources, this competition can cause
Admission Control to prevent the new tunnel from being established.
An advantage of using RSVP to establish LSP tunnels is that it solves
this problem very elegantly.
To support make-before-break in a smooth fashion, it is necessary
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Internet Draft draft-ietf-mpls-rsvp-lsp-tunnel-01.txt February 1999
that on links that are common to the old and new LSPs, resources used
by the old LSP tunnel should not be released before traffic is
transitioned to the new LSP tunnel, and reservations should not be
counted twice because this might cause Admission Control to reject
the new LSP tunnel.
The combination of the LSP_TUNNEL_IPv4 SESSION object and the SE
reservation style naturally achieves smooth transitions. The basic
idea is that the old and new LSP tunnels share resources along links
which they have in common. The LSP_TUNNEL_IPv4 SESSION object is used
to narrow the scope of the RSVP session to the particular tunnel in
question. To uniquely identify a tunnel, we use the combination of
the destination IP address, a Tunnel ID, and the sender's IP address,
which is placed in the Extended Tunnel ID field.
During the reroute operation, the source needs to appear as two
different sources to RSVP. This is achieved by the inclusion of an
"LSP ID", which is carried in the SENDER_TEMPLATE and FILTER_SPEC
objects. Since the semantics of these objects are changed, a new C-
Type is assigned.
To effect a reroute, the source node picks a new LSP ID and forms a
new SENDER_TEMPLATE. The source node then creates a new ERO to
define the new path. Thereafter the node sends a new Path Message
using the original SESSION object and the new SENDER_TEMPLATE and
ERO. It continues to use the old LSP and refresh the old Path
message. On links that are not held in common, the new Path message
is treated as a conventional new LSP tunnel setup. On links held in
common, the shared SESSION object and SE style allow the LSP to be
established sharing resources with the old LSP. Once the sender
receives a Resv message for the new LSP, it can transition traffic to
it and tear down the old LSP.
3. LSP Tunnel related Message Formats
Five new objects are defined in this section:
Object name Applicable RSVP messages
--------------- ------------------------
LABEL_REQUEST Path
LABEL Resv
EXPLICIT_ROUTE Path
RECORD_ROUTE Path, Resv
SESSION_ATTRIBUTE Path
New C-Types are also assigned for the SESSION, SENDER_TEMPLATE,
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Internet Draft draft-ietf-mpls-rsvp-lsp-tunnel-01.txt February 1999
FILTER_SPEC, FLOWSPEC objects.
Detailed descriptions of the new objects are given in later sections.
All new objects are optional with respect to RSVP. An implementation
can choose to support a subset of objects. However, the
LABEL_REQUEST and LABEL objects are mandatory with respect to this
specification.
The LABEL and RECORD_ROUTE objects, are sender specific. They must
immediately follow either the SENDER_TEMPLATE in Path messages, or
the FILTER_SPEC in Resv messages.
The placement of EXPLICIT_ROUTE, LABEL_REQUEST, and SESSION_ATTRIBUTE
objects is simply a recommendation. The ordering of these objects is
not important, so an implementation must be prepared to accept
objects in any order.
3.1. Path Message
The format of the Path message is as follows:
<Path Message> ::= <Common Header> [ <INTEGRITY> ]
<SESSION> <RSVP_HOP>
<TIME_VALUES>
[ <EXPLICIT_ROUTE> ]
<LABEL_REQUEST>
[ <SESSION_ATTRIBUTE> ]
[ <POLICY_DATA> ... ]
[ <sender descriptor> ]
<sender descriptor> ::= <SENDER_TEMPLATE> [ <SENDER_TSPEC> ]
[ <ADSPEC> ]
[ <RECORD_ROUTE> ]
3.2. Resv Message
The format of the Resv message is as follows:
<Resv Message> ::= <Common Header> [ <INTEGRITY> ]
<SESSION> <RSVP_HOP>
<TIME_VALUES>
[ <RESV_CONFIRM> ] [ <SCOPE> ]
[ <POLICY_DATA> ... ]
<STYLE> <flow descriptor list>
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Internet Draft draft-ietf-mpls-rsvp-lsp-tunnel-01.txt February 1999
Each label is an unsigned integer in the range 0 through 1048575.
The decision concerning whether to create a label stack with more
than one label, when to push a new label, and when to pop the label
stack is not addressed in this document. For implementations that do
not support a label stack, only the top label is examined. The rest
of the label stack should be passed through unchanged. Such
implementations are required to generate a label stack of depth 1
when initiating the first LABEL.
4.1.1. Handling Label Objects in Resv messages
A router uses the top label carried in the LABEL object as the
outgoing label associated with the sender. The router allocates a
new label and binds it to the incoming interface of this
session/sender. This is the same interface that the router uses to
forward Resv messages to the previous hops.
In MPLS a node may support multiple label spaces, perhaps associating
a unique space with each incoming interface. For the purposes of the
following discussion, the term "same label" means the identical label
value drawn from the identical label space. Further, the following
applies only to unicast sessions.
If a node receives a Resv message that has assigned the same label
value to multiple senders, then that node may also assign the same
value to those same senders or to any subset of those senders. Note
that if a node intends to police individual senders to a session, it
must assign unique labels to those senders.
Labels received in Resv messages on different interfaces are always
considered to be different even if the label value is the same.
To construct a new LABEL object, the router replaces the top label
(from the received Resv message) with the locally allocated new
label. The router then sends the new LABEL object as part of the
Resv message to the previous hop. The LABEL object should be kept in
the Reservation State Block. It is then used in the next Resv
refresh event for formatting the Resv message.
A router is expected to send a Resv message before its refresh timers
expire if the contents of the LABEL object change.
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Internet Draft draft-ietf-mpls-rsvp-lsp-tunnel-01.txt February 19994.1.2. Non-support of the Label Object
Under normal circumstances, a node should never receive a LABEL
object in a Resv message unless it had included a LABEL_REQUEST
object in the corresponding Path message. However, an RSVP router
that does not recognize the LABEL object sends a ResvErr with the
error code "Unknown object class" toward the receiver. This causes
the reservation to fail.
RSVP is designed to cope gracefully with non-RSVP routers anywhere
between senders and receivers. However, obviously, non-RSVP routers
cannot convey labels via RSVP. This means that if a router has a
neighbor that is not RSVP capable, the router must not advertise the
LABEL object when sending messages that pass through the non-RSVP
router. The RSVP specification [1] describes how routers can
determine the presence of non-RSVP routers.
4.2. Label Request Object
The LABEL_REQUEST object formats are shown below. Currently there
three possible C_Types. Type 1 is a Label Request without label
range. Type 2 is a label request with an ATM label range. Type 3 is
a label request with a Frame Relay label range.
Label Request without Label Range
class = 19, C_Type = 1 (need to get an official class num from
the IANA)
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved | L3PID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Reserved
This field is reserved. It must be set to zero on transmis-
sion and must be ignored on receipt.
L3PID
an identifier of the layer 3 protocol using this path.
Standard Ethertype values are used.
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Internet Draft draft-ietf-mpls-rsvp-lsp-tunnel-01.txt February 1999
Label Request with ATM Label Range
class = 19, C_Type = 2 (need to get an official class num from
the IANA)
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved | L3PID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Res | Minimum VPI | Minimum VCI |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Res | Maximum VPI | Maximum VCI |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Reserved (Res)
This field is reserved. It must be set to zero on transmis-
sion and must be ignored on receipt.
L3PID
an identifier of the layer 3 protocol using this path.
Standard Ethertype values are used.
Minimum VPI (12 bits)
This 12 bit field specifies the lower bound of a block of
Virtual Path Identifiers that is supported on the originating
switch. If the VPI is less than 12-bits it should be right
justified in this field and preceding bits should be set to
zero.
Minimum VCI (16 bits)
This 16 bit field specifies the lower bound of a block of
Virtual Connection Identifiers that is supported on the ori-
ginating switch. If the VCI is less than 16-bits it should be
right justified in this field and preceding bits should be set
to zero.
Maximum VPI (12 bits)
This 12 bit field specifies the upper bound of a block of
Virtual Path Identifiers that is supported on the originating
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Internet Draft draft-ietf-mpls-rsvp-lsp-tunnel-01.txt February 1999
switch. If the VPI is less than 12-bits it should be right
justified in this field and preceding bits should be set to
zero.
Maximum VCI (16 bits)
This 16 bit field specifies the upper bound of a block of
Virtual Connection Identifiers that is supported on the ori-
ginating switch. If the VCI is less than 16-bits it should be
right justified in this field and preceding bits should be set
to zero.
Label Request with Frame Relay Label Range
class = 19, C_Type = 3 (need to get an official class num from
the IANA)
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved | L3PID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved |DLI| Minimum DLCI |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved | Maximum DLCI |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Reserved
This field is reserved. It must be set to zero on transmis-
sion and ignored on receipt.
L3PID
an identifier of the layer 3 protocol using this path.
Standard Ethertype values are used.
DLI
DLCI Length Indicator. The number of bits in the DLCI.
The following values are supported:
Len DLCI bits
0 10
1 17
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2 23
Minimum DLCI
This 23-bit field specifies the lower bound of a block of Data
Link Connection Identifiers (DLCIs) that is supported on the
originating switch. The DLCI should be right justified in this
field and unused bits should be set to 0.
Maximum DLCI
This 23-bit field specifies the upper bound of a block of Data
Link Connection Identifiers (DLCIs) that is supported on the
originating switch. The DLCI should be right justified in this
field and unused bits should be set to 0.
4.2.1. Handling of LABEL_REQUEST
To establish an LSP tunnel the sender creates a Path message with a
LABEL_REQUEST object. The LABEL_REQUEST object indicates that a
label binding for this path is requested and provides an indication
of the network layer protocol that is to be carried over this path.
This permits non-IP network layer protocols to be sent down an LSP.
This information can also be useful in actual label allocation,
because some reserved labels are protocol specific, see [5].
The LABEL_REQUEST should be stored in the Path State Block, so that
Path refresh messages will also contain the LABEL_REQUEST object.
When the Path message reaches the receiver, the presence of the
LABEL_REQUEST object triggers the receiver to allocate a label and to
place the label in the LABEL object for the corresponding Resv
message. If a label range was specified, the label must be allocated
from that range. A receiver that accepts a LABEL_REQUEST object MUST
include a LABEL object in Resv messages pertaining to that Path
message. If a LABEL_REQUEST object was not present in the Path
message, a node MUST NOT include a LABEL object in a Resv message for
that Path message's session and PHOP.
A node that sends a LABEL_REQUEST object must be ready to accept and
correctly process a LABEL object in the corresponding Resv messages.
A node that recognizes a LABEL_REQUEST object, but that is unable to
support it (possibly because of a failure to allocate labels) should
send a PathErr with the error code "Routing problem" and the subcode
"MPLS label allocation failure." This includes the case where a
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label range has been specified and a label cannot be allocated from
that range.
If the receiver cannot support the protocol L3PID, it should send a
PathErr with the error code "Routing problem" and the subcode
"Unsupported L3PID." This causes the RSVP session to fail.
4.2.2. Non-support of the Label Request Object
An RSVP router that does not recognize the LABEL_REQUEST object sends
a PathErr with the error code "Unknown object class" toward the
sender. An RSVP router that recognizes the LABEL_REQUEST object but
does not recognize the C_Type send a PathErr with the error code
"Unknown object C_Type" toward the sender. This causes the path
setup to fail. The sender should notify management that a LSP cannot
be established and possibly take action to continue the reservation
without the LABEL_REQUEST.
RSVP is designed to cope gracefully with non-RSVP routers anywhere
between senders and receivers. However, obviously, non-RSVP routers
cannot convey labels via RSVP. This means that if a router has a
neighbor that is not RSVP capable, the router must not advertise the
LABEL_REQUEST object when sending messages that pass through the
non-RSVP routers. The router should send a PathErr back to the
sender, with the error code "Routing problem" and the subcode "MPLS
being negotiated, but a non-RSVP capable router stands in the path."
See [1] for a description of how routers can determine the presence
of non-RSVP routers.
4.3. Explicit Route Object
As stated earlier, explicit routes are to be specified through a new
EXPLICIT_ROUTE object (ERO) in RSVP Path messages. The
EXPLICIT_ROUTE object has the following format:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
// (Object contents) //
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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Class-Num
The Class-Num for an EXPLICIT_ROUTE object is 20 (need to get
an official one from the IANA with the form 0bbbbbbb to ensure
that non-supporting implementations reject the message.)
C-Type
The C-Type for an EXPLICIT_ROUTE object is 1 (need to get an
official one from the IANA)
If a Path message contains multiple EXPLICIT_ROUTE objects, only the
first object is meaningful. Subsequent EXPLICIT_ROUTE objects may be
ignored and should not be propagated.
4.3.1. Applicability
The EXPLICIT_ROUTE object is intended to be used only for unicast
situations. Applications of explicit routing to multicast are a
topic for further research.
The EXPLICIT_ROUTE object is to be used only when all routers along
the explicit route support RSVP and the EXPLICIT_ROUTE object. The
EXPLICIT_ROUTE object is assigned a class value of the form 0bbbbbbb.
RSVP routers that do not support the object will therefor response
with an "Unknown Object Class" error.
4.3.2. Semantics of the Explicit Route Object
An explicit route is a particular path in the network topology.
Typically, the explicit route is determined by a node, with the
intent of directing traffic along that path.
An explicit route is described as a list of groups of nodes along the
explicit route. Certain operations to be performed along the path
can also be encoded in the EXPLICIT_ROUTE object.
In addition to the ability to identify specific nodes along the path,
an explicit route can identify a group of nodes that must be
traversed along the path. This capability allows the routing system
a significant amount of local flexibility in fulfilling a request for
an explicit route. This capability allows the generator of the
explicit route to have imperfect information about the details of the
path.
The explicit route is encoded as a series of subobjects contained in
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an EXPLICIT_ROUTE object. Each subobject may identify a group of
nodes in the explicit route or may specify an operation to be
performed along the path. An explicit route then becomes a
specification of groups of nodes to be traversed and a set of
operations to be performed along the path.
To formalize the discussion, we call each group of nodes an abstract
node. Thus, we say that an explicit route is a specification of a
set of abstract nodes to be traversed and a set operations to be
performed along that path. If an abstract node consists of only one
node, we refer to it as a simple abstract node.
As an example of the concept of abstract nodes, consider an explicit
route that consists solely of Autonomous System number subobjects.
Each subobject corresponds to an Autonomous System in the global
topology. In this case, each Autonomous System is an abstract node,
and the explicit route is a path that includes each of the specified
Autonomous Systems. There may be multiple hops within each
Autonomous System, but these are opaque to the source node for the
explicit route.
4.3.3. Subobjects
The contents of an EXPLICIT_ROUTE object are a series of variable-
length data items called subobjects. Each subobject has the form:
0 1
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-------------//----------------+
|L| Type | Length | (Subobject contents) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-------------//----------------+
L
The L bit is an attribute of the subobject. The L bit is set
if the subobject represents a loose hop in the explicit route.
If the bit is not set, the subobject represents a strict hop in
the explicit route.
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Type
The Type indicates the type of contents of the subobject.
Currently defined values are:
0 Reserved
1 IPv4 prefix
2 IPv6 prefix
32 Autonomous system number
64 MPLS label switched path termination
Length
The Length contains the total length of the subobject in bytes,
including the L, Type and Length fields. The Length must be at
least 4, and must be a multiple of 4.
4.3.3.1. Strict and Loose Subobjects
The L bit in the subobject is a one-bit attribute. If the L bit is
set, then the value of the attribute is 'loose.' Otherwise, the
value of the attribute is 'strict.' For brevity, we say that if the
value of the subobject attribute is 'loose' then it is a 'loose
subobject.' Otherwise, it's a 'strict subobject.' Further, we say
that the abstract node of a strict or loose subobject is a strict or
a loose node, respectively. Loose and strict nodes are always
interpreted relative to their prior abstract nodes.
The path between a strict node and its preceding node MUST include
only network nodes from the strict node and its preceding abstract
node.
The path between a loose node and its preceding node MAY include
other network nodes that are not part of the strict node or its
preceding abstract node.
The L bit has no meaning in operation subobjects.
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Internet Draft draft-ietf-mpls-rsvp-lsp-tunnel-01.txt February 19994.3.3.4. Subobject 32: Autonomous System Number
The contents of an Autonomous System (AS) number subobject are a 2-
octet AS number. The abstract node represented by this subobject is
the set of nodes belonging to the autonomous system.
The length of the AS number subobject is 4 octets.
4.3.3.5. Subobject 64: MPLS Label Switched Path Termination
The contents of an MPLS label switched path termination subobject are
2 octets of padding. This subobject is an operation subobject. This
object is only meaningful if there is a LABEL_REQUEST object in the
Path message.
If a LABEL_REQUEST object is present in the Path message, this Path
message is being used to establish a label-switched path. In this
case, this subobject indicates that the prior abstract node should
remove one level of label from all packets following this label-
switched path.
The length of the MPLS label termination subobject is 4 octets.
4.3.4. Processing of the Explicit Route Object4.3.4.1. Selection of the Next Hop
A node receiving a Path message containing an EXPLICIT_ROUTE object
must determine the next hop for this path. This is necessary because
the next abstract node along the explicit route might be an IP subnet
or an Autonomous System. Therefore, selection of this next hop may
involve a decision from a set of feasible alternatives. The criteria
used to make a selection from feasible alternatives is implementation
dependent and can also be impacted by local policy, and is beyond the
scope of this specification. However, it is assumed that each node
will make a best effort attempt to determine a loop-free path. Note
that paths so determined can be overridden by local policy.
To determine the next hop for the path, a node performs the following
steps:
1) The node receiving the RSVP message must first evaluate the first
subobject. If the node is not part of the abstract node described by
the first subobject, it has received the message in error and should
return a "Bad initial subobject" error. If the first subobject is an
operation subobject, the message is in error and the system should
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return a "Bad EXPLICIT_ROUTE object" error. If there is no first
subobject, the message is also in error and the system should return
a "Bad EXPLICIT_ROUTE object" error.
2) If there is no second subobject, this indicates the end of the
explicit route. The EXPLICIT_ROUTE object should be removed from the
Path message. This node may or may not be the end of the path.
Processing continues with section 4.3.4.2, where a new EXPLICIT_ROUTE
object may be added to the Path message.
3) Next, the node evaluates the second subobject. If the subobject
is an operation subobject, the node pops the subobject from the
EXPLICIT ROUTE object , records the subobject, and continues
processing with step 2, above. Note that this changes the third
subobject into the second subobject (hence "pop") in subsequent
processing. The precise operations to be performed by this node must
be defined by the operation subobject.
4) If the node is also a part of the abstract node described by the
second subobject, then the node deletes the first subobject and
continues processing with step 2, above. Note that this makes the
second subobject into the first subobject of the next iteration and
allows the node to identify the next abstract node on the path of the
message after possible repeated application(s) of steps 2-4.
5) Abstract Node Border Case: The node determines whether it is
topologically adjacent to the abstract node described by the second
subobject. If so, the node selects a particular next hop which is a
member of the abstract node. The node then deletes the first
subobject and continues processing with section 4.3.4.2.
6) Interior of the Abstract Node Case: Otherwise, the node selects a
next hop within the abstract node of the first subobject (which the
node belongs to) that is along the path to the abstract node of the
second subobject (which is the next abstract node). If no such path
exists then there are two cases:
6a) If the second subobject is a strict subobject, there is an error
and the node should return a "Bad strict node" error.
6b) Otherwise, if the second subobject is a loose subobject, the node
selects any next hop that is along the path to the next abstract
node. If no path exists, there is an error, and the node should
return a "Bad loose node" error.
7) Finally, the node replaces the first subobject with any subobject
that denotes an abstract node containing the next hop. This is
necessary so that when the explicit route is received by the next
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hop, it will be accepted.
4.3.4.2. Adding subobjects to the Explicit Route Object
After selecting a next hop, the node may alter the explicit route in
the following ways.
If, as part of executing the algorithm in section 4.3.4.1, the
EXPLICIT_ROUTE object is removed, the node may add a new
EXPLICIT_ROUTE object.
Otherwise, if the node is a member of the abstract node for the first
subobject, a series of subobjects may be inserted before the first
subobject or may replace the first subobject. Each subobject in this
series must denote an abstract node that is a subset of the current
abstract node.
Alternately, if the first subobject is a loose subobject, an
arbitrary series of subobjects may be inserted prior to the first
subobject.
4.3.5. Loops
While the EXPLICIT_ROUTE object is of finite length, the existence of
loose nodes implies that it is possible to construct forwarding loops
during transients in the underlying routing protocol. This can be
detected by the originator of the explicit route through the use of
another opaque route object called the RECORD_ROUTE object. The
RECORD_ROUTE object is used to collect detailed path information and
is useful for loop detection and for diagnostics.
4.3.6. Non-support of the Explicit Route Object
An RSVP router that does not recognize the EXPLICIT_ROUTE object
sends a PathErr with the error code "Unknown object class" toward the
sender. This causes the path setup to fail. The sender should
notify management that a LSP cannot be established and possibly take
action to continue the reservation without the EXPLICIT_ROUTE or via
a different explicit route.
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Internet Draft draft-ietf-mpls-rsvp-lsp-tunnel-01.txt February 19994.4. Record Route Object
The format of the RECORD_ROUTE object (RRO) is as follows:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
// (Subobjects) //
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Class-Num
The Class-Num for a RECORD_ROUTE object is 21 (need to get an
official one from the IANA with the form 0bbbbbbb to ensure
that non-supporting implementations reject the message.)
C-Type
The C-Type for a RECORD_ROUTE object is 1 (need to get an offi-
cial one from the IANA)
The RRO can be present in both RSVP Path and Resv messages. If a
message contains multiple RROs, only the first RRO is meaningful.
Subsequent RROs can be ignored and should not be propagated.
4.4.1. Subobjects
The contents of a RECORD_ROUTE object are a series of variable-length
data items called subobjects. Each subobject has its own Length
field. The length contains the total length of the subobject in
bytes, including the Type and Length fields. The length must always
be a multiple of 4, and at least 4.
Subobjects are organized as a last-in-first-out stack. The first
subobject relative to the beginning of RRO is considered the top.
The last subobject is considered the bottom. When a new subobject is
added, it is always added to the top.
An empty RRO with no subobjects is considered illegal.
Two kinds of subobjects are currently defined.
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Internet Draft draft-ietf-mpls-rsvp-lsp-tunnel-01.txt February 19994.4.2. Applicability
Only the procedures for use in unicast sessions are defined here.
There are three possible uses of RRO in RSVP. First, an RRO can
function as a loop detection mechanism to discover L3 routing loops,
or loops inherent in the explicit route. The exact procedure for
doing so is described later in this document.
Second, an RRO collects up-to-date detailed path information hop-by-
hop about RSVP sessions, providing valuable information to the sender
or receiver. Any path change (due to network topology changes) is
quickly reported.
Third, RRO syntax is designed so that, with minor changes, the whole
object can be used as input to the EXPLICIT_ROUTE object. This is
useful if the sender receives RRO from the receiver in a Resv
message, applies it to EXPLICIT_ROUTE object in the next Path message
in order to "pin down session path".
4.4.3. Handling RRO
Typically, a node initiates an RSVP session by adding the RRO to the
Path message. The initial RRO contains only one subobject - the
sender's IP addresses.
When a Path message containing an RRO is received by an intermediate
router, the router stores a copy of it in the Path State Block. The
RRO is then used in the next Path refresh event for formatting Path
messages. When a new Path message is to be sent, the router adds a
new subobject to the RRO and appends the resulting RRO to the Path
message before transmission.
The newly added subobject must be this router's IP address. The
address to be added should be the interface address of the outgoing
Path messages. If there are multiple addresses to choose from, the
decision is a local matter. However, it is recommended that the same
address be chosen consistently. If the newly added subobject causes
the RRO to be too big to fit in a Path message, the Path message
shall be dropped and a PathErr message should be sent back to the
sender.
An RSVP router can decide to send Path messages before its refresh
time if the RRO in the next Path message is different from the
previous one. This can happen if the contents of the RRO received
from the previous hop router changes or if this RRO is newly added to
(or deleted from) the Path message.
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When the destination node of an RSVP session receives a Path message
with an RRO, this indicates that the sender node needs route
recording. The destination node initiates the RRO process by adding
an RRO to Resv messages. The processing mirrors that of the Path
messages. The only difference is that the RRO in a Resv message
records the path information in the reverse direction.
Note that each node along the path will now have the complete route
from source to destination. The Path RRO will have the route from
the source to this node; the Resv RRO will have the route from this
node to the destination. This is useful for network management.
A received Path message without an RRO indicates that the sender node
no longer needs route recording. Subsequent Path messages and Resv
messages shall not contain an RRO.
4.4.4. Loop Detection
As part of processing an incoming RRO, an intermediate router looks
into all subobjects contained within the RRO. If the router
determines that it is already in the list, a forwarding loop exists.
An RSVP session is loop-free if downstream nodes receive Path
messages or upstream nodes receive Resv messages with no routing
loops detected in the contained RRO.
There are two broad classifications of forwarding loops. The first
class is the transient loop, which occurs as a normal part of
operations as L3 routing tries to converge on a consistent forwarding
path for all destinations. The second class of forwarding loop is
the permanent loop, which normally results from network mis-
configuration.
The action performed by a node on receipt of an RRO depends on the
message type in which the RRO is received.
For Path messages containing a forwarding loop, the router builds and
sends a "Routing problem" PathErr message, with the subcode "loop
detected," and drops the Path message. Until the loop is eliminated,
this session is not suitable for forwarding data packets. How the
loop eliminated is beyond the scope of this document.
For Resv messages containing a forwarding loop, the router simply
drops the message. Resv messages should not loop if Path messages do
not loop.
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Internet Draft draft-ietf-mpls-rsvp-lsp-tunnel-01.txt February 19994.4.5. Non-support of RRO
The RRO object is to be used only when all routers along the path
support RSVP and the RRO object. The RRO object is assigned a class
value of the form 0bbbbbbb. RSVP routers that do not support the
object will therefor response with an "Unknown Object Class" error.
4.5. Error Subcodes for ERO and RRO
In the processing described above, certain errors must be reported as
part of a "Routing Problem" PathErr message. The value of the
"Routing Problem" error code is 24 (TBD).
The following defines the subcodes for the routing problem PathErr
message:
Value Error:
1 Bad EXPLICIT_ROUTE object
2 Bad strict node
3 Bad loose node
4 Bad initial subobject
5 No route available toward destination
6 RRO syntax error detected
7 RRO indicated routing loops
8 MPLS being negotiated, but a non-RSVP-capable router
stands in the path
9 MPLS label allocation failure
10 Unsupported L3PID
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Internet Draft draft-ietf-mpls-rsvp-lsp-tunnel-01.txt February 19994.6.4. Reroute Procedure
This section describes how to setup a tunnel that is capable of
maintaining resource reservations (without double counting) while it
is being rerouted or while it is attempting to increase its
bandwidth. In the initial Path message, the source node forms a
SESSION object, assigns a Tunnel_ID, and places its IPv4 address in
the LSP_ID. It also forms a SENDER_TEMPLATE and assigns a LSP_ID.
Tunnel setup then proceeds according to the normal procedure.
On receipt of the Path message, the destination node sends a Resv
message with the STYLE Shared Explicit to the source.
[Note: I think we should add a flag to the SESSION_ATTRIBUTE for the
source to indicate that it wishes the SE style.]
When a source node with an established path wants to change that
path, it forms a new Path message as follows. The existing SESSION
object is used. In particular the Tunnel_ID and Extended_Tunnel_ID
are unchanged. The source node picks a new LSP_ID to form a new
SENDER_TEMPLATE. It creates an EXPLICIT_ROUTE object for the new
route. The new Path message is sent. The source node refreshes both
the old and new path messages
The destination node responds with a Resv message with an SE flow
descriptor formatted as:
<FLOWSPEC><old_FILTER_SPEC><old_LABEL_OBJECT><new_FILTER_SPEC>
<new_LABEL_OBJECT>
(Note that if the PHOPs are different, then two messages are sent
each with the appropriate FILTER_SPEC and LABEL_OBJECT.)
When the Source node receives the Resv Message(s), it may begin using
the new route. It should send a PathTear message for the old route.
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Setup Priority
The priority of the session with respect to taking resources,
in the range of 0 to 7. The value 0 is the highest priority.
The Setup Priority is used in deciding whether this session can
preempt another session.
Holding Priority
The priority of the session with respect to holding resources,
in the range of 0 to 7. The value 0 is the highest priority.
Holding Priority is used in deciding whether this session can
be preempted by another session.
Name Length
The length of the display string before padding, in bytes.
Session Name
A null padded string of characters.
The support of setup and holding priorities is optional. A node can
recognize this information but be unable to perform the requested
operation. The node should pass the information downstream
unchanged.
As noted above, preemption is implemented by two priorities. The
Setup Priority is the priority for taking resources. The Holding
Priority is the priority for holding a resource. Specifically, the
Holding Priority is the priority at which resources assigned to this
session will be reserved. The Setup Priority should never be higher
than the Holding Priority for a given session.
When a new reservation is considered for admission, the bandwidth
requested is compared with the bandwidth available at the priority
specified in the Setup Priority. The bandwidth available at a
particular Setup Priority is the unused bandwidth plus the bandwidth
reserved at all Holding Priorities lower than the Setup Priority.
If the requested bandwidth is not available a PathErr message is
returned with an Error Code of 01, Admission Control Failure, and an
Error Value of 0x0002. The first 0 in the Error Value indicates a
globally defined subcode and is not informational. The 002 indicates
"requested bandwidth unavailable".
If the requested bandwidth is less than the unused bandwidth then
processing is complete. If the requested bandwidth is available, but
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is in use by lower priority sessions, then lower priority sessions
(beginning with the lowest priority) can be pre-empted to free the
necessary bandwidth.
When pre-emption is supported, each pre-empted reservation triggers a
TC_Preempt() upcall to local clients, passing a subcode that
indicates the reason. A ResvErr and/or PathErr with the code "Policy
Control failure" should be sent toward the downstream receivers and
upstream senders.
The support of fast-reroute is optional. A node may recognize the
fast-reroute Flag but may be unable to perform the requested
operation. In this case, the node should pass the information
downstream unchanged.
The support of merging is optional. A node may recognize the Merge
Flag but may be unable to perform the requested operation. In this
case, the node should pass the information downstream unchanged.
If a Path message contains multiple SESSION_ATTRIBUTE objects, only
the first SESSION_ATTRIBUTE object is meaningful. Subsequent
SESSION_ATTRIBUTE objects can be ignored and need not be forwarded.
The contents of the Session Name field are a string, typically of
displayable characters. The Length must always be a multiple of 4
and must be at least 8. For an object length that is not a multiple
of 4, the object is padded with trailing NULL characters. The Name
Length field contains the actual string length.
All RSVP routers, whether they support the SESSION_ATTRIBUTE object
or not, shall forward the object unmodified. The presence of non-
RSVP routers anywhere between senders and receivers has no impact on
this object.
4.8. Flowspec Object for Class-of-Service Service
An LSP may not need bandwidth reservations or QoS guarantees. Such
LSPs can be used to deliver best-effort traffic, even if RSVP is used
for setting up LSPs. When resources do not have to be allocated to
the LSP, the Class-of-Service service should be used.
The Class-of-Service FLOWSPEC allows indication of a Class of Service
(CoS) value that should be used when handling data packets associated
with the request.
The format of the Class-of-Service FLOWSPEC object is:
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Class-of-Service flowspec object: Class = 9, C-Type = 3 (TBA)
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved | CoS | Maximum Packet Size [M] |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Reserved
This field is reserved. It must be set to zero on transmission
and must be ignored on receipt.
CoS
Indicates the Class of Service (CoS) of the data traffic asso-
ciated with the request. A value of zero (0) indicates that
associated traffic is "Best-Effort". Specifically no service
assurances are being requested from the network. The intent is
to enable networks to support the IP ToS Octet as defined in
RFC1349 [7]. It is noted that there is ongoing work within the
IETF to update the use of the IP ToS Octet.
M
The maximum packet size parameter [M] should be set to the
value of the smallest path MTU. This parameter is set in Resv
messages by the reliever based on information in arriving RSVP
ADSPEC objects. This parameter is ignored when the object is
contained in Path messages.
5. Refresh Related Extensions
The resource requirement (in terms of cpu processing and memory) for
running RSVP on a router increases proportionally with the number of
sessions. Supporting a large number of sessions can present scaling
problems.
This section describes an approach to help alleviate one of the
scaling issues. RSVP Path and Resv messages must be periodically
refreshed to maintain state. The approach described here simply
reduces the volume of messages which must be periodically sent and
received.
One way to address the refresh volume problem is to increase the
refresh timer R. Increasing the value of R provides linear
improvement on transmission overhead, but at the cost of increasing
refresh timeout.
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An aggregate message is proposed which can reduce R for faster
detection of connectivity problems and still reduce overhead by an
order of magnitude.
A Message_ID object is defined to reduce refresh message processing
by allowing the receiver to immediately identify an unchanged
message. A Message_ACK object is defined which used in combination
with the Message_ID object may suppress refreshes altogether.
The described approach also addresses issues of latency and
reliability of RSVP Signaling. The latency and reliability problem
occurs when a non-refresh RSVP message is lost in transmission.
Standard RSVP [RFC2205] maintains state via the generation of RSVP
refresh messages. In the face of transmission loss of RSVP messages,
the end-to-end latency of RSVP signaling is tied to the refresh
interval of the node(s) experiencing the loss. When end-to-end
signaling is limited by the refresh interval, the establishment or
change of a reservation may be beyond the range of what is acceptable
for some some applications.
Finally, a hello protocol is defined to allow detection of the loss
of a neighbor node or it's RSVP state information.
5.1. RSVP Aggregate Message
An RSVP aggregate message consists of an aggregate header followed by
a body consisting of a variable number of standard RSVP messages.
The following subsections define the formats of the aggregate header
and the rules for including standard RSVP messages as part of the
message.
5.1.1. Aggregate Header
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Vers | Flags | Msg type | RSVP checksum |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Send_TTL | (Reserved) | RSVP length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The format of the aggregate header is identical to the format of the
RSVP common header [1]. The fields in the header are as follows:
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Vers: 4 bits
Protocol version number. This is version 1.
Flags: 4 bits
0x01: Aggregate capable
If set, indicates to RSVP neighbors that this node is willing
and capable of receiving aggregate messages. This bit is
meaningful only between adjacent RSVP neighbors.
0x02-0x08: Reserved
Msg type: 8 bits
12 = Aggregate
RSVP checksum: 16 bits
The one's complement of the one's complement sum of the entire
message, with the checksum field replaced by zero for the pur-
pose of computing the checksum. An all-zero value means that
no checksum was transmitted. Because individual submessages
carry their own checksum as well as the INTEGRITY object for
authentication, this field MAY be set to zero.
Send_TTL: 8 bits
The IP TTL value with which the message was sent. This is used
by RSVP to detect a non-RSVP hop by comparing the IP TTL that
an Aggregate message sent to the TTL in the received message.
RSVP length: 16 bits
The total length of this RSVP aggregate message in bytes, in-
cluding the aggregate header and the submessages that follow.
5.1.2. Message Formats
An RSVP aggregate message must contain at least one submessage. A
submessage is one of the RSVP Path, PathTear, PathErr, Resv,
ResvTear, ResvErr, or ResvConf messages.
Empty RSVP aggregate messages should not be sent. It is illegal to
include another RSVP aggregate message as a submessage.
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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Vers | Flags | 12 | RSVP checksum |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Send_TTL | (Reserved) | RSVP length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
// First submessage //
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
// More submessage... //
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
5.1.3. Sending RSVP Aggregate Messages
RSVP Aggregate messages are sent hop by hop between RSVP-capable
neighbors as "raw" IP datagrams with protocol number 46. Raw IP
datagrams are also intended to be used between an end system and the
first/last hop router, although it is also possible to encapsulate
RSVP messages as UDP datagrams for end-system communication that
cannot perform raw network I/O.
RSVP Aggregate messages should not be used if the next-hop RSVP
neighbor does not support RSVP Aggregate messages. Methods for
discovering such information include: (1) manual configuration and
(2) observing the Aggregate-capable bit (see the description that
follows) in the received RSVP messages.
Support for RSVP Aggregate messages is optional. While message
aggregation might help in scaling RSVP, and in reducing processing
overhead and bandwidth consumption, a node is not required to
transmit every standard RSVP message in an Aggregate message. A node
must always be ready to receive standard RSVP messages.
The IP source address is local to the system that originated the
Aggregate message. The IP destination address is the next-hop node
for which the submessages are intended. These addresses need not be
identical to those used if the submessages were sent as standard RSVP
messages.
For example, the IP source address of Path and PathTear messages is
the address of the sender it describes, while the IP destination
address is the DestAddress for the session. These end-to-end
addresses are overridden by hop-by-hop addresses while encapsulated
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in an Aggregate message. These addresses can easily be restored from
the SENDER_TEMPLATE and SESSION objects within Path and PathTear
messages. For Path and PathTear messages, the next-hop node can be
learned by looking up DestAddress in the forwarding table.
RSVP Aggregate messages do not require the Router Alert IP option
[RFC 2113] in their IP headers. This is because Aggregate messages
are addressed directly to RSVP neighbors.
Each RSVP Aggregate message must occupy exactly one IP datagram. If
it exceeds the MTU, the datagram is fragmented by IP and reassembled
at the recipient node. A single RSVP Aggregate message cannot exceed
the maximum IP datagram size, which is approximately 64K bytes.
5.1.4. Receiving RSVP Aggregate Messages
If the local system does not recognize or does not wish to accept an
Aggregate message, the received messages shall be discarded without
further analysis.
The receiver next compares the IP TTL with which an Aggregate message
is sent to the TTL with which it is received. If a non-RSVP hop is
detected, the number of non-RSVP hops is recorded. It is used later
in processing of sub-messages.
Next, the receiver verifies the version number and checksum of the
RSVP aggregate message and discards the message if any mismatch is
found.
The receiver then starts decapsulating individual sub-messages. Each
sub-message has its own complete message length and authentication
information. Each sub-message is processed according to procedures
specified in RFC 2209.
5.1.5. Forwarding RSVP Aggregate Messages
When an RSVP router receives an Aggregate messages which is not
addressed to one of it's IP addresses, it SHALL forward the message.
Non-RSVP routers should treat RSVP Aggregate messages as any other IP
datagram.
When individual submessages are being forwarded, they can be
encapsulated in another aggregate message before sending to the
next-hop neighbor. The Send_TTL field in the submessages should be
decremented properly before transmission.
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To support message aggregation, an additional capability bit is added
to the common RSVP header, which is defined in RFC2205 [1].
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Vers | Flags | Msg Type | RSVP Checksum |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Send_TTL | (Reserved) | RSVP Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Flags: 4 bits
0x01: Aggregate capable
If set, indicates to RSVP neighbors that this node is willing
and capable of receiving aggregate messages. This bit is
meaningful only between adjacent RSVP neighbors.
5.2. MESSAGE_ID Extension
Within the MESSAGE_ID Class there are two object types defined. The
two object types are the MESSAGE_ID object and the MESSAGE_ID ACK
object. The MESSAGE_ID Class is used to support acknowledgments and,
when used in conjunction with the Hello Extension described in
Section 5.3, to indicate when refresh messages are not needed after
an acknowledgment. When refreshes are normally generated, the
MESSAGE_ID object can also be used to simply provide a shorthand
indication of when a message represents new state. Such information
can be used on the receiving node to reduce refresh processing
requirements.
Message identification and acknowledgment is done on a hop-by-hop
basis. Acknowledgment is handled independent of SESSION or message
type. Both types of MESSAGE_ID objects contain a message identifier.
The identifier MUST be unique on a per source IP address basis across
messages sent by an RSVP node and received by a particular node. No
more than one MESSAGE_ID object may be included in an RSVP message.
Each message containing an MESSAGE_ID object may be acknowledged via
a MESSAGE_ID ACK object. MESSAGE_ID ACK objects may be sent
piggybacked in unrelated RSVP messages or in RSVP ACK messages
Either type of MESSAGE_ID object may be included in an aggregate
sub-message. When included, the object is treated as if it were
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contained in a standard, unaggregated, RSVP message. Only one
MESSAGE_ID object MAY be included in a (sub)message and it MUST
follow any present MESSAGE_ID ACK objects. When no MESSAGE_ID ACK
objects are present, the MESSAGE_ID object MUST immediately follow
the INTEGRITY object. When no INTEGRITY object is present, the
MESSAGE_ID object MUST immediately follow the (sub)message header.
When present, one or more MESSAGE_ID ACK objects MUST immediately
follow the INTEGRITY object. When no INTEGRITY object is present,
the MESSAGE_ID ACK objects MUST immediately follow the the
(sub)message header. An MESSAGE_ID ACK object may only be included
in a message when the message's IP destination address matches the
unicast address of the node that generated the message(s) being
acknowledged.
5.2.1. MESSAGE_ID Object
MESSAGE_ID Class = 166 (Value to be assigned by IANA of form
10bbbbbb)
MESSAGE_ID object
Class = MESSAGE_ID Class, C_Type = 1
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Flags | Message ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Flags: 8 bits
0x80 = ACK_Desired flag
Indicates that the sender is willing to accept a message
acknowledgment. Acknowledgments MUST be silently ignored
when they are sent in response to messages whose
ACK_Desired flag is not set. This flag MUST be set when
the Last_Refresh flag is set.
0x40 = Last_Refresh flag
Used in Resv and Path refresh messages to indicate that the
sender will not be sending further refreshes. When set,
the ACK_Desired flag MUST also be set. This flag MUST NOT
be set when the HELLO messages are not being exchanged with
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For Ack messages, the Msg Type field of the Common Header MUST be set
to 13 <TO_BE_ASSIGNED>.
5.2.3. MESSAGE_ID Object Usage
The MESSAGE_ID object may be included in any RSVP message other than
the Ack message. The MESSAGE_ID object is always generated and
processed hop-by-hop. The IP address of the object generator is
represented in a per RSVP message type specific fashion. For Path
and PathTear messages the generator's IP address is contained in the
RSVP_HOP. For Resv, ResvTear, PathErr, ResvErr, ResvConf and
Aggregate messages the generator's IP address is the source address
in the IP header.
The Message ID field contains a generator selected value. This
value, when combined with the generator's IP address, identifies a
particular RSVP message and the specific state information it
represents. When a node is sending a refresh message with a
MESSAGE_ID object, it SHOULD use the same Message ID value that was
used in the RSVP message that first advertised the state being
refreshed. When a node is sending a message that represents new or
changed state, the Message ID value MUST have a value that is not
otherwise in use. A value is considered to be in use when it has
been used in the most recent advertisement or refresh of any state
using the associated IP address. Care must also be taken to avoid
reuse of a previously used value during times of network loss. At
such times, the use of new values may not be noticed by receivers.
There is no requirement for Message ID values to be increasing or
ordered.
The ACK_Desired flag is set when the MESSAGE_ID object generator is
capable of accepting MESSAGE_ID ACK objects. Such information can be
used to ensure reliable delivery of error and confirm messages and to
support fast refreshes in the face of network loss. Nodes setting
the ACK_Desired flag SHOULD retransmit unacknowledged messages at a
faster interval than the standard refresh time until the message is
acknowledged or a "fast" retry limit is reached.
The Last_Refresh flag is set in Path and Resv messages when the
MESSAGE_ID object generator is exchanging Hello messages, described
in Section 5.3, with the next hop RSVP node. Note that the next hop
node may not be known for some Path messages. When a refresh message
with the Last_Refresh flag set is generated, normal refresh
generation MUST continue until the message containing the
Last_Refresh flag is acknowledged. Although messages removing state
advertised in such messages MUST be retransmit until acknowledged to
cover certain packet loss conditions. Messages removing state include
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PathTear and ResvTear.
Nodes receiving messages containing MESSAGE_ID objects SHOULD use the
information in the objects to aid in determining if an message
represents new state or a state refresh. Note that state is only
refreshed in Path and Resv messages. If a Path or Resv message
contains the same Message ID value that was used in the most recently
received message for the same session and, for path messages,
SENDER_TEMPLATE then the receiver SHOULD treat the message as a state
refresh. If the Message ID value differs from the most recently
received value, the receiver MUST fully processes the message.
Nodes receiving a message containing a MESSAGE_ID object with the
ACK_Desired flag set, SHOULD respond with a MESSAGE_ID ACK object.
If a node supports the Hello extension it MUST also check the
Last_Refresh flag of received Resv and Path messages. If the flag is
set, the receiver MUST NOT timeout state associated with associated
message. The receiver MUST also be prepared to properly process
refresh messages.
5.2.4. MESSAGE_ID ACK Object Usage
The MESSAGE_ID ACK object is used to acknowledge receipt of messages
containing MESSAGE_ID objects that were sent with the ACK_Desired
flag set. The Message ID field of a MESSAGE_ID ACK object MUST have
the same value as was received. A MESSAGE_ID ACK object MUST NOT be
generated in response to a received MESSAGE_ID object when the
ACK_Desired flag is not set.
A MESSAGE_ID ACK object may be sent in any RSVP message that has an
IP destination address matching the generator of the associated
MESSAGE_ID object. The MESSAGE_ID ACK object will not typically be
included in the non hop-by-hop Path, PathTear and ResvConf messages.
When no appropriate message is available, one or more MESSAGE_ID ACK
objects SHOULD be sent in an Ack message. Implementations SHOULD
include MESSAGE_ID ACK objects in standard RSVP messages when
possible.
Upon receiving a MESSAGE_ID ACK object for a message generated with
the No_Refresh flag set, normal refresh generation SHOULD be disabled
for the associated state. When normal refresh generation is
suppressed for Path and Resv state, special care must be taken to
remove such state. Particularly in the case of possible packet loss.
To ensure such state is removed, once a node generates a Path or Resv
refresh message containing a MESSAGE_ID object with the No_Refresh
flag set, the node MUST retransmit until acknowledged all messages
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removing such state. Messages removing state include PathTear and
ResvTear.
5.2.5. Multicast Considerations
Path and PathTear messages may be sent to IP multicast destination
addresses. When the destination is multicast, it is possible that a
single message containing a single MESSAGE_ID object will be received
by multiple RSVP next-hops. When the ACK_Desired flag is set in this
case, acknowledgment processing is more complex. There are a number
of issues including ACK implosion, number acknowledgments to be
expected and handling new receivers.
ACK implosion occurs when each receiver responds to the MESSAGE_ID
object at approximately the same time. This can lead to a
potentially large number of MESSAGE_ID ACK objects simultaneously
delivered to the message generator. To address this case, the
receiver MUST wait a random interval prior to acknowledging a
MESSAGE_ID object received in a message destined to a multicast
address. The random interval SHOULD be between zero (0) and a
configured maximum time. The configured maximum SHOULD be set in
proportion to the refresh and "fast" retransmission interval.
A more fundamental issue is the number of acknowledgments that the
upstream node, the message generator, should expect. The number of
acknowledgments that should be expected is the same as the number of
RSVP next-hops. In the router-to-router case, the number of next-
hops can usually be obtained from routing. When hosts are either the
upstream node or the next-hops, the number of next-hops will
typically not be readily available. When the number of next-hops is
not known, the message generator SHOULD only expect a single response
and MUST ignore the No_Refresh flag of MESSAGE_ID Ack objects. The
result of this behavior will be special retransmission handling until
the message is delivered to at least one next-hop, then followed by
standard RSVP refreshes. Standard refresh messages will synchronize
state with any next-hops that don't receive the original message.
Another issue is handling new (host or router) receivers. It is
possible that after sending a Path message and handling of expected
number of acknowledgments that a new receiver joins the group. In
this case a new Path message must be sent to the new receiver. When
normal refresh processing is occurring, there is no issue. When
normal refresh processing is suppressed, a path message must still be
generated. In the router-to-router case, the identification of new
next-hops can usually be obtained from routing. When hosts are
either the upstream node or the next-hops, the identification of new
next-hops will typically not be possible. When identification of new
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next-hops is not possible, the message generator SHOULD only expect a
single response and MUST ignore the No_Refresh flag of MESSAGE_ID Ack
objects. The result of this behavior will be special retransmission
handling until the message is delivered to at least one next-hop,
then followed by standard RSVP refreshes. Standard refresh messages
will synchronize state with any next-hops that don't receive the
original message.
There is one additional minor issue with multiple next-hops. The
issue is handling a combination of standard-refresh and non-refresh
next-hops, i.e. Hello messages are being exchanged with some
neighboring nodes but not with others. When this case occurs,
refreshes MUST be generated per standard RSVP and the Last_Refresh
flag MUST NOT be set.
5.2.6. Compatibility
There are no backward compatibility issues raised by the MESSAGE_ID
Class. The MESSAGE_ID Class has an assigned value whose form is
10bbbbbb. Per RSVP [1], classes with values of this form must be
ignored and not forwarded by nodes not supporting the class. When
the receiver of a MESSAGE_ID object does not support the class, the
object will be silently ignored. The generator of the MESSAGE_ID
object will not see any acknowledgments and therefore refresh
messages per standard RSVP. Lastly, since the MESSAGE_ID ACK object
can only be issued in response to the MESSAGE_ID object, there are no
possible issues with this object or Ack messages.
Implementations supporting the MESSAGE_ID extension MUST also support
the Hello extension.
5.3. Hello Extension
The RSVP Hello extension enables RSVP nodes to detect a loss of a
neighboring node's state information. In standard RSVP, such
detection occurs as a consequence of RSVP's soft state model. When
refresh message generation is disabled via the previously discussed
No_Refresh flag processing, the Hello extension is needed to address
this failure case. The Hello extensions is not intended to provide a
link failure detection mechanism, particularly in the case of
multiple parallel unnumbered links.
The Hello extension is specifically designed so that one side can use
the mechanism while the other side does not. Neighbor RSVP state
tracking may be initiated at any time. This includes when neighbors
first learn about each other, or just when neighbors are sharing Resv
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or Path state. All implementations supporting the MESSAGE_ID ACK
object MUST also support the Hello Extension. Such implementations
SHOULD initiate Hello processing and MUST be able to respond to Hello
messages.
The Hello extension is composed of a Hello message, a HELLO REQUEST
object and a HELLO ACK object. Hello processing between two
neighbors supports independent selection of, typically configured,
failure detection intervals. Each neighbor can autonomously issue
HELLO REQUEST objects. Each request is answered by an
acknowledgment. Hellos also contain enough information so that one
neighbor can suppress issuing hello requests and still perform
neighbor failure detection.
Neighbor state tracking is accomplished by collecting and storing a
neighbor's state "instance" value. If a change in value is seen,
then the neighbor is presumed to have reset it's RSVP state. The
HELLO objects provide a mechanism for polling for and providing an
RSVP state instance value. A poll request also includes the sender's
instance value. This allows the receiver of a poll to optionally
treat the poll as an implicit poll response. This optional handling
is an optimization that can reduce the total number of polls and
responses processed by a pair of neighbors. In all cases, when both
sides support the optimization the result will be only one set of
polls and responses per failure detection interval. Depending on
selected intervals, the same benefit can occur even when only one
neighbor supports the optimization.
5.3.1. Hello Message Format
Hello Messages are always sent between two RSVP neighbors. The IP
source address is the IP address of the sending node. The IP
destination address is the IP address of the neighbor node.
The Hello message format is as follows:
<Hello Message> ::= <Common Header> [ <INTEGRITY> ]
<HELLO>
For Hello messages, the Msg Type field of the Common Header MUST be
set to 14 <TO_BE_ASSIGNED>.
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This is done by comparing the sender's Instance field value with the
previously received value. If the value differs, than the neighbor
has reset and all state associated with the neighbor MUST be
"expired" and cleaned up per standard RSVP processing.
On receipt of a message containing a HELLO ACK object, the receiver
MUST verify that the neighbor has not reset. This is done by
comparing the sender's Instance field value with the previously
received value. If the value differs, than the neighbor has reset
and all state associated with the neighbor MUST be "expired" and
cleaned up per standard RSVP processing.
5.3.4. Compatibility
The Hello extension is fully backwards compatible. The Hello class
is assigned a class value of the form 0bbbbbbb. Depending on the
implementation, implementations that don't support the extension will
either silently discard Hello messages or will respond with an
"Unknown Object Class" error. In either case the sender will fail to
see an acknowledgment for the issued Hello. When a Hello sender does
not receive an acknowledgment, it MUST NOT send MESSAGE_ID ACK
objects with the No_Refresh flag set to the corresponding RSVP
neighbor. This restriction will preclude neighbors from getting out
of RSVP state synchronization.
Implementations supporting the Hello extension MUST also support the
MESSAGE_ID extension.
6. Acknowledgments
This document contains ideas as well as text that have appeared in
previous Internet Drafts. The authors of the current draft wish to
thank the authors of those drafts. They are Steven Blake, Bruce
Davie, Roch Guerin, Sanjay Kamat, Yakov Rekhter, Eric Rosen, and Arun
Viswanathan. We also wish to thank Bora Akyol, Yoram Bernet and Alex
Mondrus for their comments on this draft.
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